The present invention relates to apparatus for dispensing materials, including, for example, an air-operable gun for dispensing thermoplastic and thermosetting plural component materials, such as urethane foams and coatings, catalyzed polyesters, catalyzed epoxies and other chemical compositions that react rapidly upon mixing of the components thereof.
Polyurethane foam systems, for example, usually include component A, an isocyanate, and component B, a preformulated compound comprising a polyether resin, a catalyst, a surfactant and a blowing agent. Each component of the plural material is, by itself, generally stable, that is, each component does not cure or cross-link for several months or more, provided it is properly stored. However, mixing of component A and component B in proper concentrations initiates a chemical reaction that causes the components to begin to polymerize and generate heat which volatilizes the blowing agent and causes the polyurethane to foam, cure and cross-link. In one polyurethane system, water is used to combine with isocyanate to provide a carbon dioxide blowing agent; and in another polyurethane system, a fluorocarbon or freon, which boils at about room temperature, provides the blowing agent. In this system, the blowing agent is trapped in the resin and acts in cooperation with the other constituents of the system to foam the polyurethane. Other systems may be such that the blowing agent is used to provide a cellular structure.
Usually cross-linking and curing of a plural component material is substantially completed in a matter of seconds. It is therefore desirable to mix the components in the dispensing device as close as is possible to the orifice from which the mix is ejected, that is, mixing of the several components of the compound should take place substantially contemporaneously with dispensing. Mixing the components of the plural component material with the dispensing device requires the apparatus operator to purge the residue of the mixed components from a mixing chamber and the orifice of the dispensing device so that the residue components do not chemically react and clog the chamber and the orifice, or in any other way prevent or inhibit dispensing of the plural component material.
U.S. Pat. No. 3,799,403, issued to Richard O. Probst et al. discloses an apparatus for mixing and dispensing plural component materials, such as urethane foam materials. The Probst et al. patent discloses a hand gun which includes a mixing and dispensing element that is movable with respect to the housing of the device between a rearward position, at which the components of the plural component material are introduced into a mixing chamber in the mixing and dispensing element, appropriately mixed and then dispensed, and a forward position, at which the introduction of components into the mixing chamber is terminated, and air is introduced into the mixing chamber to substantially purge residue material from the mixing chamber and its cooperatively associated orifice.
In the gun disclosed by the Probst et al. patent, the movable mixing and dispensing element forms, in combination with a pair of connection blocks carried by the gun housing, the valves that control the mixing and dispensing of the plural component material. The connection blocks are connectible with the separate pressurized sources of the components of the plural component material and include outlet openings and carry plastic seal members around the outlet openings that interface with and seal against the sides of the mixing and dispensing orifice. The movable mixing and dispensing element includes an internal mixing chamber between its sides, a pair of admission openings, one between each side of the mixing and dispensing element and its internal mixing chamber, and a forward-most dispensing orifice connected with the mixing chamber. When the mixing and dispensing orifice is in its rearward position, the admission openings on each of its sides are aligned with the outlet openings of the connection blocks so the components of the plural component material can flow from their separate pressurized sources into the mixing chamber, where they are mixed and urged out of the dispensing orifice. When the mixing and dispensing element is in its forward position, the outlet openings of the connection blocks are blocked by the sides of the mixing and dispensing element, terminating the dispensation of mixed plural component materials. In the rearward position, the seals carried by the connection blocks confine the flows of the plural components to between the connection block-outlet openings and the admission openings of the mixing and dispensing element, and in the forward position, the seals prevent the plural components from flowing into the interface between the mixing and dispensing element and the connection blocks.
The housing of the device disclosed by the Probst et al. patent includes an air-operated piston/cylinder that is connected to the mixing and dispensing element to move it between its forward and rearward positions. A trigger on the handle of the hand gun controls the application of compressed air, through a four-way valve, to the portions of the cylinder on each side of a piston to move it forwardly and rearwardly within the cylinder, thus moving the mixing and dispensing element between its rearward mixing and dispensing position and its forward position at which the flow of plural component material is terminated and the mixing chamber is purged.
Plural component guns like those disclosed in the Probst et al. patent have been sold for almost 30 years by Glas-Craft, Inc., with the registered trademark PROBLER(copyright). Such guns have required periodic replacement of the plastic seals that become worn through use as a result of the movement of the mixing and dispensing element against the seals, and it is desirable to reduce the intervals between seal replacement and apparatus down time. While it would be desirable to replace the plastic seals with metal seals to extend the seal life, the substantial increase in friction between the metal seals and the mixing and dispensing element could not be reliably overcome by an air operated piston/cylinder unit without unacceptably increasing the size and weight of the gun and reducing its maneuverability. In addition, in the event of a seal failure, or an improper seal replacement, or an improper attachment of connection blocks, or warped or damaged connection blocks, the plural components of the plural component material were sometimes urged by the pressure of their sources to flow into the piston/cylinder actuator where they reacted, terminating operation of the gun and requiring its disassembly and cleaning.
The invention provides, for example, as an improvement of the PROBLER(copyright) gun, an air-operated, plural component dispensing hand gun with substantially improved reliability, reduced down time, and substantially reduced maintenance requirements without a significant increase in cost, size, weight or maneuverability of the gun.
A plural component hand gun of the invention comprises, for example, a housing, a pair of component connection blocks, each with a component outlet, carried by the housing, and a mixing and dispensing element, with admission openings for the plural components, carried by the housing between the connection blocks and forming, with the connection blocks, valves for controlling the flow of the components, a pair of metal seal elements carried at the component outlets between the connection blocks and the mixing and dispensing element, and an air-actuator for controlling the flow of plural component material from the hand gun comprising two serially connected pistons operating along a common axis within two separate cylinder portions of the housing, said serially connected pistons being connected with said mixing and dispensing element and driven in the same direction along a common axis of the two separate cylinder portions by the application of compressed air to the two separate cylinder portions
A preferred apparatus of the invention can include, for example, a housing including a connection portion at its forward end and an actuator portion at its rearward end; a mixing and dispensing element formed with a planar portion on each of its sides, a mixing chamber within the element between the planar side portions of the element, a pair of admission openings, one admission opening extending between each of the planar sides of the element and the mixing chamber, and a dispensing orifice connected with the mixing chamber at the forward end of the mixing and dispensing element, said mixing and dispensing element being slidably carried by the connection portion of the housing; a pair of connection blocks for the plural components, one connection block being carried on each side of the connection portion of the housing with a side surface interfacing with a planar side portion of the mixing and dispensing element, each connection block providing means for connecting a supply of one of the plural components with the mixing chamber of the mixing and dispensing element and including an internal supply passageway leading to an outlet opening in its side surface, the side surface of each of said connection blocks carrying a seal element around its outlet opening that slidably engages the interfacing planar side portion of the mixing and dispensing element and seals the interface between the connection block and the mixing and dispensing element; and an air-operated actuator carried by the actuator portion of the housing for sliding the mixing and dispensing element with respect to the connection portion of the housing between a rearward position at which the admission openings of the mixing and dispensing element communicate with the outlet openings of the connection blocks, permitting a flow of the plural components into the mixing chamber for mixing and dispensation, and a forward position at which the outlet openings of the connection blocks are blocked by the planar side portions of the mixing and dispensing element, said air-operated actuator comprising a cylinder-forming wall within the actuator portion of the housing and a dual piston element slidably carried within the cylinder-forming wall and extending forwardly for connection with the mixing and dispensing element, said dual piston element comprising a forward piston and a rearward piston, each slidably sealed with the cylinder-forming wall, and a cylinder-dividing element slidably carried by a connecting rod extending between the forward and rearward pistons, said cylinder-dividing element being sealed with and held stationary within the cylinder-forming wall of the actuator portion of the housing, whereby the actuator portion of the housing is provided with a first piston/cylinder portion with the forward piston being drivable therein and a second piston/cylinder portion with the rearward piston being drivable therein, the driving forces of said forward piston and rearward piston being combined in sliding the mixing and dispensing element between its forward and rearward positions.
Embodiments of the invention can further comprise means for connecting a compressed air inlet in the housing with a source of compressed air, comprising a first opening in communication with air passageways leading to the two separate cylinder portions of the actuator portion of the housing, a second opening in communication with an air passageway leading to an air chamber formed so as to be adjacent the admission openings of the mixing and dispensing element in its forward non-dispensing position, and a ball check valve between the first and second openings which is opened in the presence of compressed air at the first opening and closed in the absence of compressed air at the first opening, thereby preventing plural component material from flowing back into the first opening and the air passageways leading to the air-operated actuator and its operating valve.
The drawings and more detailed description of the preferred embodiment that follow comprises one example of the invention. Other embodiments of the invention will be apparent to those skilled in the art from the drawings and more detailed description that follows.